Foucault
In the late twentieth century, Michel Foucault expanded the concept of genealogy into a counter-history of the position of the subject which traces the development of people and societies through history. His genealogy of the subject accounts "for the constitution of knowledges, discourses, domains of objects, and so on, without having to make reference to a subject which is either transcendental in relation to the field of events or runs in its empty sameness throughout the course of history."As Foucault discussed in his essay "Nietzsche, Genealogy, History", Foucault's ideas of genealogy were greatly influenced by the work that Nietzsche had done on the development of morals through power. Foucault also describes genealogy as a particular investigation into those elements which "we tend to feel [are] without history". This would include things such as sexuality, and other elements of everyday life. Genealogy is not the search for origins, and is not the construction of a linear development. Instead it seeks to show the plural and sometimes contradictory past that reveals traces of the influence that power has had on truth.
As one of the important theories of Michel Foucault, genealogy deconstructs truth, arguing that truth is, more often than not, discovered by chance, backed up by the operation of Power/knowledge or the consideration of interest. Therefore, all truths are questionable. Pointing out the unreliability of truth, which is often accused as "having tendency of relativity and nihilism", the theory flatly refuses the uniformity and regularity of history, emphasizing the irregularity and inconstancy of truth and toppling the notion that history progresses in a linear order.
The practice of genealogy is also closely linked to what Foucault called the "archeological method:"
In short, it seems that from the empirical observability for us of an ensemble to its historical acceptability, to the very period of time in which it is actually observable, the analysis goes by way of the knowledge-power nexus, supporting it, recouping it at the point where it is accepted, moving toward what makes it acceptable, of course, not in general, but only where it is accepted. This is what can be characterized as recouping it in its positivity. Here, then, is a type of procedure, which, unconcerned with legitimizing and consequently excluding the fundamental point of view of the law, runs through the cycle of positivity by proceeding from the fact of acceptance to the system of acceptability analyzed through the knowledge-power interplay. Let us say that this is, approximately, the archaeological level [of analysis].